This invention relates to blow molding, and in particular it relates to increasing the production rate of a cold parison blow molding apparatus.
Numerous products such as foods, liquid soaps, etc. are now packaged and sold in non-breakable containers, generally referred to as "plastic bottles". These containers, which are commonly made from a polyolefin such as polyproplylene are normally manufactured, inter alia, by extruding the material into an elongated endless hollow tube and then cutting this tube into sections, referred to as parisons, and blow molding these parisons into finished articles. While numerous different materials may be used, for convenience this application will refer specifically to polypropylene.
The two basic procedures for forming parisons into finished articles are known as the hot parison technique wherein the extruded parisons, while still hot from the extrusion process, are cut into sections and immediately blow molded, and the cold parison technique wherein the extruded tube is cut into parisons which are then stored and then at a subsequent point in time reheated and blow molded into finished articles. A feature of this cold parison technique includes stretching of the heated parisons just prior to blow molding thereof.
In my copending application Ser. No. 276,071, filed July 28, 1972, now U.S. Pat. No. 3,765,813, issued on Oct. 16, 1973, which is a continuation of my earlier application Ser. No. 3003, filed Jan. 15, 1970, now abandoned, there is described a new and improved cold parison blow molding method and apparatus. In that basic arrangement, the parisons are placed on a conveyor and moved through an oven for a period of time sufficient to heat the parisons to the proper forming temperature, whereupon a transfer arm removes the heated parisons and transfers the same to a blow mold.
While the arrangement of my said previous application represents a major step forward in the art of cold parison blow molding, there exists a continuing need for new and improved arrangements, especially for increasing the output rate per unit of machine cost.
The present invention is an improvement of my said earlier patent and consequently my said earlier U.S. Pat. No. 3,765,813 is incorporated herein for all of the details described therein, the present specification being directed essentially to the improvements thereof.
One possible arrangement for increasing the production rate of any blow molding apparatus is to provide a plurality of blow molds on a rotating frame. Such an arrangement is shown for example as applied to the formation of disc shaped preforms into wide mouth containers in my earlier U.S. Pat. No. 3,661,489, issued May 9, 1972. For details of such a rotary multiple blow molding arrangement, per se, my said earlier U.S. Pat. No. 3,661,489 is incorporated herein by reference.